A rechargeable secondary battery is generally classified into hard cap batteries and internal batteries. FIG. 1 shows a representative example of the hard cap battery. Referring to FIG. 1, a hard cap battery 10 is provided as a detachable part of a device 12, and thus has an advantage of convenience in mounting of the battery to the device 12. However, since the hard cap battery 10 requires a case (housing) 11 that serves to house a battery body embedded therein and is designed to have a shape according to a kind of an associated device, it has problems of higher price and incompatibility.
On the other hand, since an internal battery 20 is used in a state of being embedded within the device and covered by a case constituting a part of the device, as shown in FIG. 2, it has advantages of lower prices and compatibility in spite of its inconvenience in mounting of the battery to the device.
FIGS. 3 and 4 show the detailed construction of the internal battery. Referring to FIGS. 3 and 4, the internal battery 20 comprises: a battery body 21 that is provided, for example, at one side with a cathode terminal and at the other side with an anode terminal; a protective circuit (PTC) element 22 connected to one of the terminals of the battery body 21 to primarily protect the battery from over-current, over-discharge, and over-charge; a protective circuit module 24 connected to the terminal connected to the PTC element 22 through a nickel plate 23 and to the other terminal of the battery body through a nickel plate 27 to secondarily protect the battery, the protective circuit module 24 including outer input and output terminals formed on an outer surface of the protective circuit module 24 for allowing an associated device (not shown) to be connected to the protective circuit module 24; upper and lower cases 25 and 26 enclosing the battery body 21, the PTC element 22, and the protective circuit module 24.
Insulating sheets 28 are disposed between a side surface of the battery body 21 and the nickel plate 23, and between the protective circuit module 24 and the nickel plate 27, and thus prevent shorting due to unnecessary contact between the respective nickel plates 23 and 27 and adjacent battery body 21 or the protective circuit module 24.
Additionally, a double-sided adhesive tape is disposed between the battery body 21 and the lower case 26, allowing the battery body 21 to be intimately fixed to the bottom surface of the lower case 26. Accordingly, when the battery body 21 is received within the upper and lower cases 25 and 26, it can be stably fixed within the cases 25 and 26.
In order to manufacture the battery as described above, after a battery assembly is inserted into a battery can 30, a cap 31 is mounted on an opening of the can 30, and coupled thereto by laser welding around a contact portion between the cap and the opening. Then, an electrolyte is injected into the can 30 through an injection port 32 formed at one side of the cap 31.
However, the secondary battery constructed as described above has some problems.
First, there is an increasing demand for a smaller and lighter battery as a result of miniaturization and compactness of devices, and thus it is necessary to manufacture a case corresponding to such a battery through an ultra-precise thin film injection molding, which has a technological difficulty and results in an increase of manufacturing costs.
Second, the secondary battery requires a number of processes for mounting the PTC element, the nickel plates, the protective circuit module, the upper and lower cases, and the like, and is difficult to assemble, thereby providing high frequency of defective products and increasing the manufacturing costs.
Third, since the upper and lower cases are mainly welded to each other through supersonic welding, it is necessary for the pack to have a predetermined thickness or more for the supersonic welding, which becomes a factor of impedance to the miniaturization and compactness of the battery. Further, since minute movement of the upper and lower cases occurs during the supersonic welding, defectiveness of the products is high, and constant operator management is necessary.
As for an approach for solving the problems as described above, an approach has been suggested, in which a number of components (that is, a cap assembly) mounted on the upper end of the battery body is insert injection molded together with the battery body. FIGS. 5 to 7 is a diagram illustrating such an insert injection molding method, a front view and a side view illustrating a secondary battery manufactured by the method, respectively.
Referring to FIGS. 5 to 7, the battery 20 is manufactured in such a manner that, with a connection terminal 50 at the side of the protective circuit module 24 being connected to a lid 51 at the side of the battery body 21, the protective circuit module 24 and the battery body 24 of the battery 20 are integrally fixed to each other within a molding space 40 of a mold 43 comprising an upper mold 41 and a lower mold 42 by means of a molten resin (not shown) injected through an injection port 44 of the upper mold 41.
Such an insert injection molding method for manufacturing the battery 20 does not requires the upper and lower cases, and thus has an advantage of reducing the dimensions (in particular, the thickness) of the battery. However, since a cap assembly 60 is molded integrally with the battery body 21 within the mold 40, this method has several problems as follows.
First, since the battery body 21 and the protective circuit module 24 are fixed within the molding space 43 by the molten resin in a state wherein a circuit is operated by positioning the battery body 21 containing an electrode assembly together with the protective circuit module 24 within the molding space 43 of the mold 40, there is a high possibility of short due to contact of the battery body 21 and the protective circuit module 24 to the mold 40 while they are integrally fixed within the mold 24. Accordingly, since the battery body 21 and the protective circuit module 24 constitute the circuit with power applied thereto, there is inconvenience in that the output terminal must be coated in order to prevent electrical short.
Second, if the battery body 21 is deformed due to pressure applied thereto according to the size of the battery body 21 or if the molten resin having a high temperature and a high pressure is injected into the molding space 43 while coupling the upper mold 41 and the lower mold 42 with the battery body 21 temporarily joined to the protective circuit module 24 within the molding space 43 of the mold 40, misalignment between the battery body 21 and the protective circuit module can easily occur during the injection of the molten resin into the molding space 43, thereby increasing the frequency of defective products.
Third, if the battery body 21 has a high temperature within the molding space 40, the battery can be susceptible to change in electrical characteristics and be subjected to a danger of explosion. Additionally, in the event when a pressure is applied to the battery can constituting the battery body 21 within the mold 40, the pressure can be applied to the portion where the battery can and the cap are welded to each other, thereby creating an un-welded portion.
Accordingly, the internal battery has several problems, such as movement of the internal components due to the injection molding together with the battery body 21, instability of the contact surface of the battery body 21 and the resinous molding portion, and dimensional preciseness of the battery body 21 for allowing the battery body 21 to be inserted into the mold 40, and the like.